A report into cycling's troubled past is "scandalously biased", says former International Cycling Union (UCI) president Hein Verbruggen.
Verbruggen and fellow ex-UCI boss Pat McQuaid were criticised by a Cycling Independent Reform Commission review.
And Verbruggen has also accused current president Brian Cookson of having an "obsession" with removing him as honorary president.
Cookson has said he will not be drawn into "this kind of public conflict".
"Mr Cookson is in for a surprise if he thinks that I will accept this scandalously biased Circ report, and the same goes for taking away my honorary title," said Dutchman Verbruggen.
"Indeed, the last word about the Circ report has not yet been written."
In a statement, Cookson said: "I think Mr Verbruggen's letter speaks for itself. Those who have read the Circ report will understand where the UCI went wrong in the past, including the conflicts it needlessly got into and which seriously damaged its credibility.
"I was elected to change the way the UCI conducts itself and I won't be drawn into this kind of public conflict."
In a letter of more than 3,000 words, published in Belgian newspaper De Morgen, Verbruggen has also:
- accused Cookson of making "comical" attempts to avoid a face-to-face meeting
- suggested that UCI director general Martin Gibbs is the organisation's real "acting" president
- instructed Swiss lawyers to assess the Circ report
- roundly dismissed the report's findings as "lacking any factual basis for many of the opinions contained in it".
Cookson's election as UCI president in 2013 was achieved after a manifesto which promised to investigate consistent accusations of corruption in the organisation, as well as the fallout of the Lance Armstrong doping scandal.
That investigation came in the form of Circ's findings in March, which accused Verbruggen - who served as president between 1991 and 2005 - and his successor McQuaid of failing to follow their own anti-doping rules as well as showing preferential treatment to Armstrong.